Primary amoebic meningoencephalitis is a fulminating human infection associated with swimming activities in naturally or artificially heated waters that harbor virulent Naegleria amoebae. Most of the isolations of pathogenic Naegleria species have been made from habitats altered or disturbed by human activity. Verification of the occurrence of these amoebae in disturbed habitats will significantly contribute to our understanding of their ecology and distribution and help to identify potential hazardous sources of infection. In addition, investigation of the factor(s) associated with pathogenicity and of the biochemical principles that permit the growth of these organisms at elevated temperatures will contribute to a better understanding of these mechanisms in all pathogenic and/or thermophilic organisms. The research methodology will be to 1) sample hot springs that have been altered or disturbed to various degrees by human activity and compare the amoebae populations with hot springs that are relatively undisturbed; 2) conduct intensive sampling for the detection of pathogenic Naegleria; 3) test the feasibility of using commercially available enzyme detection systems for the identification of thermophilic Naegleria; 4) observe the effect of pigments from thermophilic bacteria on the growth and viability of Naegleria; 5) compare the phospholipase(s) and cytotoxic factor(s) from virulent and attenuated strains of pathogenic Naegleria.